1. Field of the Invention
The present invention relates to an electrophoretic display in which a dispersion containing electrophoretic particles is enclosed into a plurality of divided cells partitioned by a bulkhead and to a method for producing the electrophoretic display.
2. Related Art of the Invention
Electrophoretics utilizing electrophoresis phenomenon have been known as devices of non-luminous type. The electrophoresis is a phenomenon where particles (electrophoretic particles) migrate due to a Coulomb""s force when applying an electric field to a dispersion composed of liquid (dispersion medium) in which the particles are dispersed.
Fundamentally, the electrophoretic display has two electrodes facing each other at a predetermined length gap and dispersion inserted between the electrodes. When applying a potential difference to both electrodes, charged electrophoretic particles are pulled to either of the electrodes by the electric field generated between the electrodes. The electrode to which the particles are pulled depends on the direction of the electronic field. The dispersion medium is dyed with a dye and the electrophoretic particles are made from pigment particles, with the result that an observer can view the color of either electrophoretic particles or dye. Therefore, from a principle point of view, patterning one of the electrodes and controlling voltage applied to the electrodes enables images to be displayed.
However, since the dispersion is made of liquid, that is, flowing fluid, the electrophoretic particles scatter even when a pattern is made on an electrode, thereby resolution in display being deteriorated. To avoid such a drawback, there has been proposed a technique by a Japanese Patent Publication No. 49-32038. This publication discloses a configuration in which a bulkhead is arranged to enclose dispersion into divided minute cells. Thus electrophoretic particles contained in the dispersion are allowed to move only within each cell.
The above publication fails to disclose, however, how to fill the dispersion into each of the divided cells. Thus, electrophoretics could not be produced based on the configuration disclosed by the above patent publication.
An object of the present invention, which has been made to overcome such a situation that the conventional technique encounters, is to provide an electrophoretic display and a method for producing the same which are able to fill dispersion into each divided cell.
To achieve the above object, the present invention provides a method for producing an electrophoretic display, the method comprising a process of providing a bulkhead on a substrate so as to partition a space on the substrate into a plurality of divided cells; and a process of ejecting dispersion containing electrophoretic particles toward an opening of the bulkhead as a droplet, to charge the divided cells with the dispersion. In this method, the dispersion is ejected toward an opening of the bulkhead as a droplet, thereby each divided cell being charged with the dispersion. Because the dispersion is ejected into the divided cells as a droplet, the dispersion can be charged in a steady manner even when the divided cells are minute in size. For ejecting droplets of the dispersion, an ink jet type of ejection apparatus can be used. This enables mass production of electrophoretics with greatly shorter pixel pitches and higher fineness in display under high reliability of manufacturing.
In a preferred embodiment, the method for producing an electrophoretic display, comprising a process of providing a bulkhead on a first substrate so as to partition a space on the substrate into a plurality of divided cells; a process of ejecting a dispersion containing electrophoretic particles toward an opening of the bulkhead as a droplet, to charge the divided cells with the dispersion; a process of sealing the opening of the bulkhead with a sealer; and a process of applying a second substrate to the sealed first substrate. In this method, after the dispersion is charged into each divided cell, the opening of the bulkhead is sealed, which makes it possible to securely keep the dispersion within the divided cells. Once charged in the divided cells, there is no fear that the dispersion may leak therefrom. In addition, since no extraneous material is mixed into the dispersion, its intermediate products are easier to handle, thus providing an improved yield.
In the above production method, the method may further comprise processes of forming, on one of surfaces of the first substrate, a plurality of data lines, a plurality of scanning lines, a plurality of switching elements each placed according to each of intersections made between the scanning lines and the data lines, and a plurality of pixel electrodes each electrically connected with each switching element, the processes being carried out before the bulkhead is formed on the one of the surfaces of the first substrate. For instance, thin film transistors can be used as the switching elements. The data lines, scanning lines, and switching elements can be formed on the substrate in the processes of production of the apparatus.
In the above production method, it is preferred that the second substrate is transparent, and the method further comprises a process of forming a transparent common electrode onto the second substrate before the second substrate is applied to the sealed first substrate. This makes it possible to manufacture an active matrix type of electrophoretic display. Further, because both of the common electrode and the second substrate are made to be transparent, the second substrate has a surface on which the common electrode is not formed, so the surface can be used as a display surface.
It may also be configured that conductivity is partly or entirely given to the bulkhead, of which conductive part is used as a common electrode paired with the pixel electrodes. It may also be configured that the sealer may have conductivity and be used as a common electrode paired with pixel electrodes. It may also be configured that the sealing process includes a process of sealing the opening of the bulkhead using a non-conductive sealer employed as the sealer, and a process of giving conductivity to the non-conductive sealer. Moreover, after the opening of the bulkhead is sealed with a non-conductive sealer employed as the sealer, conductivity may be given to the non-conductive sealer, then the sealed first substrate may be applied to the second substrate. These embodiments cause the process to form the common electrode to be omitted.
In the foregoing production method, another alternative is that either one of a plurality of row electrodes or a plurality of column electrodes are formed on one of surfaces of the first substrate, and the other of the plurality of row electrodes and the plurality of column electrodes are formed on the second substrate in advance, wherein the bulkhead is formed onto the one of the surfaces of the first substrate. This method allows one to produce a passive matrix type of electrophoretic display.
For forming the bulkhead by using the foregoing production method, an alternative may be adopted in which, in the ejecting, a material of the bulkhead is ejected toward the first substrate as the droplet, thereby the bulkhead being formed. In this case, an ink jet type of ejecting apparatus can be used as a droplet ejecting apparatus. This enables a bulkhead material to be layered at a desired location with high precision, providing a minutely structured bulkhead.
Further, in forming the bulkhead by using the foregoing production method, it is preferred that the bulkhead is formed by pressing a material of the bulkhead with a stamper. This method makes it possible to manufacture finely structured bulkheads with higher productivity.
In the foregoing production method, an alternative may be configured such that a plurality of data lines, a plurality of scanning lines, a plurality of switching elements each placed according to each of intersections made between the scanning lines and the data lines, and a plurality of pixel electrodes each electrically connected with each switching element are previously formed on the second substrate, and the bulkhead formed by the stamper is applied to the first substrate to form the bulkhead on the first substrate.
Preferably, the first substrate is transparent, and on the first substrate is formed a transparent common electrode paired with the pixel electrode. Thus, an active matrix type of electrophoretic display can be manufactured.
It may also be configured that the sealer may have conductivity and be used as a common electrode paired with pixel electrodes.
A further configuration may be formed in a manner that a material of the bulkhead is a sheet-like conductive member covered by a resin member, the material of the bulkhead is pressed with the stamper so that the divided cells are formed on one of surfaces of the conductive member, thereby the bulkhead being produced, and the bulkhead is applied to the first substrate so as to form the bulkhead on the first substrate, in which the conductive member is used as a common electrode paired with the pixel electrodes. In this configuration, the common electrode can be manufactured concurrently with manufacturing of the bulkhead with the stamper, with the result that the manufacturing processes can be simplified.
Also, another configuration may be formed in a manner that a plurality of data lines, a plurality of scanning lines, a plurality of switching elements each placed according to each of intersections made between the scanning lines and the data lines, and a plurality of pixel electrodes each electrically connected with each switching element are previously formed on the second substrate, the bulkhead formed by the stamper is coated partly or entirely with a conductive material, in which a part of the bulkhead, which is coated with the conductive material, is used as a common electrode paired with the pixel electrodes, and the coated bulkhead is applied to the first substrate so that the bulkhead is formed on the first substrate. In this case, the process to form the common electrode can be removed.
Also, another configuration may be formed in a manner that the bulkhead is partly or entirely arranged at a boundary of pixels. When arranged at the entire boundary, the pixels are able to correspond to the divided cells one by one. This will lead to manufacturing of electrophoretics capable of visualizing high-quality images.
Also, another configuration may be formed in a manner that the bulkhead is formed with a bulkhead material which is black. In the case of display in colors, a black matrix is used. When the bulkhead is composed of a black bulkhead material in such a case, the bulkhead and the black matrix can be used in common, so that a process to form the black matrix can be omitted.
Also, another configuration may be formed in a manner that the sealer is made of material to be fluidized by heating, in which the sealer is disposed at the opening of the bulkhead, and the opening of the bulkhead is sealed by heating the disposed sealer. According to the present invention, mixed bubbles in charging the dispersion can be expelled out by heating, thus improving a charging rate of the dispersion. An electrophoretic display capable of displaying high-quality images can therefore be manufactured.
Also, another configuration may be formed in a manner that the sealer is made of material not to be mixed with the dispersion, wherein the sealer is coated or spayed on the first substrate in which the dispersion is charged and the opening of the bulkhead is sealed by hardening the sealer. This configuration makes it possible to place the sealer on the dispersion without a gap. Therefore, electrophoretic displays capable of displaying images in high quality can be manufactured.
Still, it is preferred that the sealer is made of material greater in relative gravity than the dispersion and not to be mixed with the dispersion, wherein the dispersion to which the sealer is added is ejected toward each of the divided cells when the dispersion is ejected as a droplet, thereby both of the dispersion and the sealer being charged into the cells, and then the opening of the bulkhead is sealed by hardening the sealer when the dispersion and the sealer are separated from each other in each of the divided cells. This configuration can exclude a gap between the sealer and the dispersion. Additionally, a process to coat or spray the sealer can be omitted. It is therefore possible to manufacture an electrophoretic display capable of displaying high-quality images in higher productivity.
Another configuration may be realized in a manner that a porous sheet having a plurality of pores is made to adhere to the first substrate on which the bulkhead is formed, wherein the dispersion is ejected, as the droplet, through the pores toward the first substrate to which the porous sheet adheres, and the pores are sealed by ejecting the sealer as a droplet toward each pore. In this case, since a thickness of the dispersion is dependent on the porous sheet, the thickness can be uniform over the entire screen. In consequence, it is possible to manufacture an electrophoretic display which has a capability to visualize high-quality images with no irregularities in depiction.
According to another aspect of the present invention, there is provided an electrophoretic display for performing a desired display by changing a spatial state of electrophoretic particles pixel by pixel, comprising a bulkhead partitioned into a plurality of divided cells and disposed partly or entirely at a boundary of the pixels, dispersion containing the electrophoretic particles to be charged into each of the plurality of divided cells, and a pair of electrodes fixedly sandwiching the dispersion, at least one electrode being transparent. In this invention, the bulkhead is located at boundaries of pixels, so that a decrease in a numerical aperture, which lowers dependently on a thickness of the bulkhead, can be minimized.
In this configuration, if the display is made on a plurality of different hues each assigned to each pixel in accordance with a predetermined rule, it is preferred that the bulkhead is disposed at least at a boundary of pixels whose display hues are different from each other. This allows display in colors. Alternatively, it is preferred that the bulkhead is black, because the bulkhead can be used in common with a black matrix.
In the foregoing electrophoretic display, it is preferable to comprise a sealer for sealing the charged dispersion. It is also preferred that the sealer has conductivity and consists of the one electrode used in common with the sealer. Still, preferable is that the bulkhead has conductivity in partly or entirely, part of the bulkhead, which has conductivity, being used in common with the one electrode.
Alternatively, the foregoing electrophoretic display may be configured in such a way that it comprises a first substrate on which a plurality of data lines, a plurality of scanning lines, a plurality of switching elements each disposed correspondingly to an intersection made between each scanning line and each data line, and a plurality of pixel electrodes each electrically connected with each switching element, and a second substrate on which a common electrode is formed, wherein the bulkhead is fixedly sandwiched between the first and second substrates, the one electrode being the common electrode and the other electrode being the pixel electrodes. Accordingly, this configuration is able to provide an active matrix type of electrophoretic display of which numerical aperture is higher.
Alternatively, the foregoing electrophoretic display may have a first substrate on which a plurality of first electrodes are placed and a second substrate on which a plurality of second electrodes are placed, wherein the bulkhead is fixedly sandwiched between the first and second substrates. This configuration is able to provide a passive matrix type of electrophoretic display of which numerical aperture is higher.
As another aspect of the present invention, there is provided an electric device provided with one of the foregoing various types of electrophoretic displays. By way of example, the electric device is an electronic book, personal computer, portable phone, electronic advertisement board, electronic road sign, or others.